Just so you know, thorns doesn't stack. You only need it on 1 piece of armor.

Sadly, this isn't true. Each piece needs thorns for the thorns effect. If you're chest plate has thorns, and you get hit in the chest plate, then the attacker will receive damage. But, if he hits you in the head, he won't receive damage, as there is no thorns on that piece of armor. Bump!

In addition, you only need one piece of thorns. But, having Thorns on all 4 pieces will result in a definite hit, compared to a 45% chance. In conclusion, Thorns on all pieces is very helpful... helpful times 4.